1. Field of the Invention
This invention relates to an object recognition apparatus that can be used in an automatic driving controller suitable for cruising on a highway, for example. In particular, the present invention relates to an improvement of a technique for recognizing two or more vehicles driving ahead.
2. Description of Related Art
Conventionally, autopilot apparatuses are used in various ships for automatically steering the ships. Such autopilot apparatuses are mainly used when ships cruise on the open sea, and when the weather is bad or when running in difficult locations such as inside harbors; the ships are steered by navigators.
Similarly, automatic driving apparatuses for vehicles are now being studyied as is disclosed in Japanese Patent Application, First Publication, No. Hei 10-283462. However, because the conditions of roads varies due to the environment, and the number of vehicles running on the roads, there are many difficulties in developing an automatic driving apparatus for vehicles in comparison to the autopilot apparatuses for ships.
However, it is difficult for ordinary drivers to maintain concentration when driving vehicles on long and monotonous roads such as highways, and it is well known that such monotonous conditions may easily cause snoozing during driving. Therefore, in the case such as long-distance drive on a highway, the load on the driver can be decreased if vehicles can be driven by automatic driving apparatuses in areas, excluding, entrances and exits on highways.
In addition, when an automatic driving apparatus includes a navigation system using GPS (Global Positioning System) geodetic satellites, it is possible to store a driving route in advance in the automatic driving apparatus. In this case, because the automatic driving apparatus stores the driving route in advance, by continuously locating the present position using the navigation system, it becomes possible to drive the vehicle to the goal if conditions are suitable.
Moreover, in the areas where the vehicle density is high in comparison to the vehicle capacity of the roads, such as in Japan, it is easy to find a preceding vehicle running ahead of the subject vehicle. Therefore, as another type of automatic driving apparatus, an automatic driving apparatus for automatically following such a preceding vehicle is also studied. In this case, if a suitable preceding vehicle can be found, it becomes possible to perform automatic driving without complicated calculation in consideration of other vehicles.
As a device for detecting preceding vehicles or obstacles which can be used in those automatic driving apparatuses, a timesharing type FM radar system using millimeter band waves and a send and receive antenna is proposed in Japanese Patent No. 2,567,332. This FM radar system receives reflected waves reflected by a preceding vehicle or an obstacle, measures the distance between the present vehicle and the detected target based on differential time between the transmission and the reception of signal, and calculates relative speed with respect to the present vehicle based on the Doppler shift of the reflected signal. Furthermore, in this system, by providing a plurality of antennas for emitting a plurality of beams having the same radiation pattern toward a plurality of directions, it is possible to detect the direction to the preceding vehicle or the obstacle.
In general, behaviors of vehicles such as maximum speeds and decelerating characteristics when braking are various due to the kinds of vehicles, for example, trucks or passenger cars. Therefore, it is desirable when performing automatic driving to detect the kinds of vehicles ahead. However, the above-mentioned radar system can detect only a vehicular gap, a relative speed, and direction to the preceding vehicle, and there is a problem that it cannot recognize the kind of detected vehicle.
In addition, when two or more preceding vehicles are running side by side, the conventional radar system recognizes these vehicles as one large vehicle.
Furthermore, when the subject, or present vehicle is running on a center lane and two preceding vehicles are running respectively on right and left lanes, if the distance to the preceding vehicles is large, although the center lane is empty, the radar system sometimes recognizes that one vehicle is running ahead. Therefore, although the present vehicle can pass by the preceding vehicles while running the center lane, the present vehicle would be controlled to follow the preceding vehicles with a constant vehicle gap, and there is a problem that this behavior would interfere the subsequent vehicles and inhibit smoothness of the traffic.
The first object of the present invention is to provide an object recognition apparatus that can distinguish the kinds of the preceding vehicles or obstacles.
The second object of the present invention is to provide an object recognition apparatus which can determine, when two or more vehicles are running side by side ahead of the present vehicles, that these are different kind of vehicles.
The third object of the present invention is to provide an object recognition apparatus which can determine, when two vehicles are running respectively on right lane and left lane ahead of the present vehicles, that the center lane is empty.
The first aspect of the present invention is an object recognition apparatus which comprises an antenna which emits transmission beams toward a plurality of directions; a receiving circuit which receives reflected signals of the transmission beams from predetermined directions; a distance and direction calculation circuit which calculates distance and direction to objects reflecting the transmission beams based on the transmission beams and the reflected signals; an object pattern storage unit which stores range direction patterns of reflected signals obtained in advance with respect to predetermined objects; an object recognition circuit which compares range direction patterns of the reflected signals received by the receiving circuit with respect to the predetermined directions, with the range direction patterns stored in the object pattern storage unit, and which recognize that a pair of reflected signals from two neighboring directions are signals reflected by the same object.
In this object recognition apparatus, the object pattern storage unit stores range direction patterns of reflected signals which are obtained in advance with respect to objects having various shapes. These objects may be rear portions of predetermined vehicles, and in this case, it is possible to determine the kinds of preceding vehicles using the stored range direction patterns. The range direction patterns may be determined based on the length of each of the predetermined vehicles, that is, the length of the range direction patterns may be the values corresponding to the standard length of the vehicles to be registered. In this case, it is possible to reduce the data amount to be stored in the object pattern storage unit while enabling the determination of the kind of vehicles.
The transmission beam is preferably FM waves in the range of 60 to 77 GHz. By using FM waves, the distance to objects can be calculated based on time difference between the transmission and reception of the FM waves, and furthermore, relative speed of the object can be determined based on the Doppler shift of the reflected waves.
The pluralities of transmission beams are preferably emitted in an angular range of 10 to 20 degrees with respect to the forward direction of the antenna. In this case, sufficient information can be obtained in order to drive a vehicle on a highway automatically. Several of the transmission beams are preferably three to nine. If the number of transmission beams is two, it is difficult to obtain a resolving power sufficient for automatic driving of vehicles. The transmission beams may be pulse radar or laser radar.
The object recognition circuit recognizes that two reflected waves that come from neighboring directions and have the same range directional pattern are reflected by the same object. Therefore, such as when a truck and a passenger car are running side by side, if reflected waves, which come from neighboring directions, have range directional patterns different from each other, the object recognition circuit can determine that two different vehicles are running side by side.
In the case where the object recognition circuit is constructed so as to recognize each object in consideration of the normal widths of various vehicles which are registered in advance in the object pattern storing unit and the like, even if, for example, two sedan type cars are running side by side, the object recognition circuit can determine that two sedan type cars are running side by side.
The object recognition apparatus according to the second aspect of the present invention comprises an antenna which emits transmission beams toward a plurality of directions; a receiving circuit which receives reflected signals of the transmission beams from predetermined directions; a distance and direction calculation circuit which calculates distance and direction to objects reflecting the transmission beams based on the transmission beams and the reflected signals; a frequency computing circuit which calculates frequency spectrums of the reflected signals from predetermined directions; a clustering processing circuit which compares with each other the frequency spectrums of the reflected signals obtained with respect to the predetermined directions, and which recognizes that reflected signals having similar frequency spectrums are signals reflected by the same object.
In this case, if a similar section is found in the frequency spectrums corresponding to two neighboring reflected signals, the clustering processing circuit performs clustering of the two signals as the signals reflected by the same object. In this way, the clustering processing circuit compares reflection spectrums of all neighboring directions, and performs clustering of signals that are determined to be reflected by the same object. Thus, this object recognition apparatus can recognize that two vehicle are running ahead of the present vehicle even when two different types of vehicles are running side by side ahead of the present vehicle.